Firstly, Tasmanian agricultural areas (soil) have a mean annual temperature of 11-13 deg C. So I can expect the concrete foundation to sit at about 14-16 deg year round. When the house is built adding a few deg for ambient heat in the house. I have shown that this system will hold 150 watt load at about +7 deg above concrete temperature.

So I can expect water for my PC cooling loop to be about 21-23 deg C year round. I was hoping for a bit lower in the range of 16 deg and I'm sure this would be possible with a longer loop.

After all those variables are taken into account. I can expect to have chilled water 8-10 deg C below my current water loop which should give me quite a lot more head room for overclocking and best of all NO NOISY FANS blasting air through a heat exchanger.

A big thanks to the people that posted constructive comments and offered help with this project